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ABSTRACT: Chert Within the Lisburne Group, North Slope, Alaska: Implications for Regional Diagenesis

Julie A. Kupecz, David L. Boyer

Chert is a ubiquitous constituent of Mississippian-Pennsylvanian Lisburne Group carbonates in both outcrop and subsurface of the North Slope, Alaska. Petrographic analysis allows the documentation of at least four major chert types and a final pore-filling megaquartz.

The earliest chert within the Lisburne selectively replaces crinoid ossicles. This is followed by nodular cherts that replace grainstones/packstones (peloidal, oolitic, bioclastic, spicular, and rare radiolarian), as well as lime mudstones/wackestones. Nodular cherts are of at least two generations. The first generation predates pre-Permian erosion, and the second postdates late-stage dolomitization, dedolomitization, and calcite cementation of fractures. These are followed by pore-filling chert and pore-filling megaquartz.

Many chert types within the Lisburne display characteristic microporosity and are a likely source for abundant microporous cherts observed within the Triassic Ivishak Formation. Although cherts are volumetrically minor as a reservoir constituent within the Lisburne, oversized pores created by the virtually complete dissolution of Ivishak microporous chert clasts may locally play a significant role in hydrocarbon production. In turn, it is possible that late pore-filling quartz within the Lisburne was derived from this later dissolution of Ivishak microporous cherts. This process appears to be associated with the expulsion of hot acidic fluids preceding hydrocarbon generation and subsequent migration. Therefore, study of microporosity formation and evolution in Lisburne cherts allows i sight into the diagenetic history of the Lisburne and also into the regional diagenetic history of the North Slope.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990